In recent years, thermal ink transfer has been used for printing output data of computers, word processors and the like. In general, in the formation of images, letters and the like by the thermal ink transfer, a thermal transfer sheet, formed by coating a thermally transferable ink onto a substrate in the form of a 2 to 20 .mu.m-thick polyethylene terephthalate film to form a thermally transferable ink layer, is provided, and the thermal transfer sheet is heated by means of a thermal head from the backside of the substrate to transfer the thermally transferable ink layer onto an image-receiving sheet.
Among image receiving sheets used in the formation of images, letters and the like by the thermal ink transfer are those that, after formation of images, letters and the like, are applied to other objects. In this type of image receiving sheets, a pressure-sensitive adhesive layer and a release sheet are laminated onto an image receiving substrate on its side remote from an image receiving surface, and, after the formation of images, letters and the like by thermal ink transfer, the release sheet is separated, followed by application to other object through the pressure-sensitive adhesive layer.
In the conventional image receiving sheet, the release sheet comprises paper which has been subjected to release treatment. Therefore, the image receiving surface of the image receiving substrate has low surface smoothness due to influence of surface irregularities of the release sheet. This is likely to cause dropouts or voids at the time of transfer. Further, the image receiving sheet, when used after storage under high temperature and high humidity conditions, unfavorably absorbs moisture and is deformed, resulting in lowered print quality.